1. Field of the Invention
The present invention relates to an inter-block interface circuit and system LSI.
2. Description of the Related Art
There are techniques for setting circuitry for low power consumption mode to reduce power consumption in apparatuses such cellular telephones that demand severe decreases in power consumption.
In general, the power consumption becomes zero when the power supply of the entire circuitry is completely interrupted, but waiting time is necessary to enable the circuitry to operate when the power supply is turned on again.
Accordingly, in the low power consumption mode, it is general to set circuitry for non-operation state (for example, by interrupting a signal input to prohibit level changes in signal line) or to suspend power supply in part of the circuitry, instead of turning off the power supply of the entire circuit (for example, an entire macro-block).
In recent years, increases in scale in system LSI have been progressed, and such a tendency has been pronounced that a plurality of different types of circuits that are conventionally constructed as IC individually is integrated onto a single semi-conductor substrate.
Increasing the scale in system LSI is extremely effective in reducing the packing area, and as the size is reduced, further decreases in power consumption are expected. For example, in mobile terminals such as cellular telephones, the battery life is decreased corresponding to accelerated increases in multifunctionality and rate, and market demands for low power consumption become more severe.
Thus, in large-scale system LSI mounted on devices such as mobile terminals, there is a fear that following conventional low power consumption mode techniques cannot adequately respond to the demands for decreases in power consumption.
Therefore, beyond conventional common sense, the inventor of the present invention examined enhancement in power consumption reducing function by precisely controlling power supply in each of a plurality of different types of blocks (macroblocks) integrated on a system LSI to implement turning off the entire block.
In the case of a system LSI, since a plurality of different types of functional blocks are packaged, there is a high possibility that blocks are present which do not need to be ON at the same time corresponding to usage of the blocks and necessity of cooperation of the blocks, and therefore, it is considered to enable increases in power consumption reduction effect by controlling the power supplies of such blocks precisely to turn off timely.
Further, since in recent years there have been power supply voltages under 3V and decreases in power supply voltage are remarkable as compared to times when 5V power supply is uniformly used, the time required for the voltage to reach a predetermined value is reduced even when the power supply that has been turned off once is turned on, and in this respect, controlling ON/OFF of the power supply of each block is considered as taking advantages.
However, when turning on or off the power supply of each block independently, for example, in the case where a path is present to communicate signals between adjacent blocks, suspension of all the circuits of blocks whose power supplies are turned off causes the potential of the path to be unsteady, and there is a fear that such unsteady potential causes two transistors composing a CMOS inverter to be ON at the same time and the shoot-through current is thus generated.
As measures against such a case, there is known a technique for providing a signal path with a gate circuit to compulsively fix an output of the gate circuit. In order to use such a technique, a power supply that is always ON (i.e. a power supply that is not switched on or off) is necessary.
However, the presence of the always-ON power supply is contradictory to the demands for power consumption reduction, and carrying out wiring of such a power supply (power supply wiring) increases restrictions in layout and also causes increases in chip size.
Further, since each block packaged on a single substrate is switched on or off at irregular intervals, the relative relationship between a switched-off block and switched-on block changes always, which is an obstacle to taking measures.